Dual circular polarization flat plate antenna that uses multilayer structure with meander line polarizer

ABSTRACT

An apparatus performs dual circular polarization in a flat plate antenna simultaneously, and does not require more than two meander line polarization layers. A first linear polarization layer and a second linear polarization layer including a polarization power divider ( 2, 4 ) and a radiation panel ( 3, 5 ) positioned on the polarization power divider ( 2, 4 ), are provided to respectively perform first and second senses of linear polarization. Additionally, a first meander line polarizer layer ( 6 ) is positioned on the second linear polarization layer and a second meander line polarizer layer ( 7 ) is positioned on the first meander line polarizer layer. The first and second meander line polarizer layers ( 6, 7 ) convert linear polarization signals into a circular polarization signals.

This application claims the benefit of U.S. Provisional Application Nos.60/283,916 and 60/283,917, filed Apr. 13, 2001, under 35 U.S.C. §119(e).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention disclosure relates to a low-cost flat plateantenna for direct broadcasting systems (DBS) and other low costapplications, and more specifically, a two-layer meander-line polarizeris used to simultaneously produce two senses (i.e., components) oforthogonal circular polarizations.

2. Background of the Invention

In the related art, two orthogonal senses of linear polarization in amultilayer printed circuit structure can be produced, as well as asingle circular polarization using a multilayer printed circuitstructure. The related art single circular polarization implementationincludes a special radiating element with perturbation segments and asingle point feeding or a linear polarization antenna with at least 3 to4 layers of a meander line polarizer.

However, the related art does not disclose or suggest use of dual linearpolarization antenna with a meander line polarizer. More specifically,the use of two meander line layers to convert the linear polarizationinto a circular polarization for a single or dual senses of circularpolarization has not been demonstrated as achievable in the related art.Thus, the aforementioned related art structure has at least thedisadvantage of requiring extra layers in the printed circuit antenna,which results in an increased cost, if production of an output havingtwo orthogonal senses is desired.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome at least theaforementioned problems and disadvantages of the related art system.

It is another object of the present invention to minimize a number oflayers present in a multilayer structure of a flat plate antenna, thusminimizing cost and size of the flat plate antenna.

To achieve at least the above objects, an apparatus for performing dualcircular polarization in a flat plate antenna is provided, comprising alinear polarizer configured to perform a first sense and a second senseof a linear polarization, and generate linear polarization outputs, anda meander line polarizer positioned on the linear polarization structureand having a first layer stacked on a second layer. In this apparatus,the meander line polarizer generates circular polarization signals basedon the linear polarization outputs.

Additionally, a method of performing dual circular polarization isprovided, comprising the steps of (a) performing a first sense of linearpolarization to generate a first linearized output, and (b) performing asecond sense of linear polarization to generate a second linearizedoutput The method further comprises the step of (c) receiving the firstlinearized output and the second linearized output in a two-layermeander line polarizer to generate circular polarization signals.

Further, a flat plate antenna configured to perform dual circularpolarization is provided, comprising an apparatus for performing dualcircular polarization. The apparatus includes a first linearpolarization layer configured to perform a first sense of a linearpolarization, a second linear polarization layer, positioned on thefirst linear polarization layer, configured to perform a second sense ofthe linear polarization, a first meander line polarizer layer positionedon the second linear polarization layer, and a second meander linepolarizer layer positioned on the first meander line polarizer layer.The first meander line polarizer layer and the second meander linepolarizer layer convert linear polarization signal outputs from thefirst linear polarization layer and the second linear polarization layerinto circular polarization signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of illustrative, nonlimiting embodiments of the presentinvention and are incorporated in and constitute a part of thisspecification, illustrate embodiments of the invention and together withthe description serve to explain the principles of the presentinvention.

FIG. 1 illustrates a multilayer structure of a dual circular polarizerflat plate antenna according to an exemplary embodiment of the presentinvention;

FIG. 2 illustrates a configuration of the meander line polarizer layersaccording to the exemplary embodiment of the present invention;

FIG. 3 illustrates a graphical representation of a measured axial ratioof the meander line polarizer over 500 MHz bandwidth according to thepresent invention; and

FIG. 4 illustrates a graphical representation of a measured axial ratioof the meander line polarizer over 2 GHz bandwidth according to thepresent invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to an illustrative, non-limitingembodiment of the present invention, examples of which are illustratedin the accompanying drawings. In the present invention, the terms aremeant to have the definition provided in the specification, and areotherwise not limited by the specification.

The present invention includes a low-cost flat plate antenna that uses atwo-layer meander-line polarizer to simultaneously produce two senses oforthogonal circular polarizations. The multiple-layer printed-circuitantenna includes a first set and a second set of linear polarizationlayers stacked on one another. The respective outputs of the first andsecond sets of the linear polarizer layers are the respective orthogonallinear polarizations. Additionally, a first and second meander-linepolarizer layer are stacked together, on the top of the stacked (i.e.,dual) linear polarization layers. The meander line polarizer layersintroduce the phase shifts and signal decomposition, which leads to twosets of orthogonal linear polarizations at phase quadratures to producetwo senses of orthogonal circular polarizations. The arrangement of theabove-disclosed layers is described in greater detail below with respectto the drawings.

As a result, low axial ratios (e.g., approximately 1 to 2 dB) can beobtained over antenna beam width and over a wide frequency band (e.g.,greater than about 20%). Also, the minimization of the number of printedcircuit layers by having only two meander line polarizer layers resultsin the reduction of production cost of the antenna.

The printed circuit layers of the exemplary embodiment of the presentinvention are used as the feed lines, radiating elements and polarizerfor the antenna device. Also, the two-layer meander line polarizerconverts the array dual linear polarization into dual circularpolarization. The design of the array and the two-layer polarizer canalso be scaled to different frequency bands.

FIG. 1 shows the multilayer structure of the flat plate antenna thatsimultaneously produces dual circular polarizations, according to anexemplary embodiment of the present invention. A bottom layer that is aground plane 1 is provided. Further, four printed circuit layers 2, 3,4, 5 are stacked above the ground plane as feeding lines and radiatingelements for the two orthogonal linear polarizations (i.e., linearpolarization A and B). For example, but not by way of limitation, afirst power dividing network 2 (i.e., power divider) and a firstradiation panel 3 are disclosed for polarization network A, and a secondpower dividing network 4 and a second radiation panel 5 are disclosedfor polarization network B.

As further illustrated in FIG. 1, two printed circuit layers 6, 7 arefirst and second layers of the meander line polarizer, which convert thelinear polarization signals into circularly polarized signals (i.e.,circular polarization A and B), and are stacked on top of the stackedprinted circuit layers 2, 3, 4, 5. In the present invention, low-lossfoam layers (e.g., 8) separate the printed circuit layers from oneother. Thus, the two senses of linear polarization pass through thetwo-layer meander line polarizer independently to simultaneously producetwo orthogonal senses of circular polarization (i.e., right hand senseRHCP and left hand sense LHCP).

FIG. 2 shows a front view of the meander line polarizer layers 6, 7according to the preferred embodiment of the present invention. Themeander line conductive strip arrays 9, 11 are distributed homogeneouslyon respective thin dielectric substrates 10, 12. The two meander linelayers 6, 7 are separated by the low loss foam layer (e.g., 8), as shownin FIG. 1. FIG. 2 further illustrates that the meander line conductivestrip arrays 9, 11 on each of the respective meander line layers 6, 7are printed at a 45° angle with respect to the polarization direction ofthe linearly polarized wave.

FIG. 3 illustrates the measurement results of the axial ratio over theapproximately 500 MHz bandwidth for the meander line polarizer. In FIG.3, the maximum value is about 1 dB. Further, FIG. 4 illustrates themeasured value of the axial ratio for approximately 2 GHz bandwidth, amaximum of which is about 2 dB.

In addition to the foregoing illustrative description, the followingadditional description is provided. The two meander line polarizerlayers may also be separated by a distance that is less than one quarterwavelength. For example, but not by way of limitation, the distance is0.15 of a wavelength. As noted above, the meander line polarizer layersintroduce phase shifts and signal decomposition, which leads todecomposing the signals into two sets of orthogonal linear polarizationsat phase quadratures to produce circular polarizations.

Each array has a plurality of parallel conductive strips, and each stripis formed with a periodic and substantially square wave pattern thatfollows a longitudinal axis. The meander line strip arrays 9, 11 aredistributed homogeneously on a major surface of their respective thindielectric substrates 10, 12, which are made of Mylar in an exemplaryembodiment.

The structure of each meander-line strip array 9, 11 is designed to bepredominantly inductive to one linear polarization and predominantlycapacitive to the orthogonal linear polarization. Accurate spacingbetween two meander-line layers or sheets 6, 7 can be achieved by usinglow loss polyfoam as the dielectric 8 (i.e., the foam layer) at adesired thickness. The structure of the polarizer can convert linear tocircular polarization according to the following principle. The incidentlinearly polarized wave can be resolved into two equal linearlypolarized components at ±45° relative to the incident wave. The meanderlines on each of the respective polarizer layers are oriented at 45°relative to the incident wave. The two orthogonal components arein-phase when incident on the polarizer. On passing through thepolarizer, one component goes through an inductive phase change, whilethe orthogonal component goes through a capacitive phase change. If aphase shift of 90° is achieved by the two wave components when they passthrough the polarizer, a circularly polarized wave is generated.

A first width of the conductive material in the meander-line array is awidth of the conductor in the longitudinal direction of the metalizedline on the plane of the layers 6, 7, while a second width is thedimension of the conductor in a direction orthogonal to the longitudinaldirection. The height of the meander-line, which is the spacing betweenthe apicies of the periodic square wave, is measured in the plane of themeander line layer 6, 7, while the period of the meander line isidentified as A. The first and second width parameters and the height Bdetermine the operating frequency and the bandwidth of the polarizer.The distance between each meander-line 2, 3 in each respective array 6,7 determines the phase shift of each layer. For circuit matchingpurposes, layer 6 and layer 7 have different parameter values, but arenot limited thereto. While a square wave pattern is preferred,modifications to such periodic pattern may be utilized, as would beknown to one skilled in the art.

The present invention has various advantages over the related art. Forexample, but not by way of limitation, it is an advantage of the presentinvention that the number of layers in the printed circuit antenna isreduced from the related art requirement of at least 3 layers to 2layers, which translates into a reduction of cost.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the described illustrativeembodiments of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover all modifications and variations of this inventionconsistent with the scope of the appended claims and their equivalents.

1. An apparatus for performing dual circular polarization in a flatplate antenna, comprising: a linear polarization structure configured toperform a first sense and a second sense of a linear polarization, andgenerate linear polarization outputs; a meander line polarizerpositioned on said linear polarization structure and having a firstlayer stacked on a second layer, wherein said meander line polarizergenerates circular polarization signals based on said linearpolarization outputs.
 2. The apparatus of claim 1, said linearpolarization structure comprising: a first linear polarization layerconfigured to perform said first sense of said linear polarization; anda second linear polarization layer, positioned on said first linearpolarization layer, and configured to perform said second sense of saidlinear polarization.
 3. The apparatus of claim 2, further comprising atleast one foam layer positioned between each of said first linearpolarization layer, said second linear polarization layer and said firstlayer and said second layer of said meander line polarizer.
 4. Theapparatus of claim 2, wherein each of said first linear polarizationlayer and said second linear polarization layer comprises: apolarization power divider; and a radiation panel positioned on saidpolarization power divider.
 5. The apparatus of claim 4, furthercomprising said at least one foam layer positioned between saidpolarization power divider and said radiation panel of each of saidfirst linear polarization layer and said second linear polarizationlayer.
 6. The apparatus of claim 1, further comprising a ground planepositioned on a surface of said linear polarization structure andopposite said meander line polarizer.
 7. The apparatus of claim 1,wherein said first sense comprises a left hand circular polarizationcomponent, and said second sense comprises a right hand circularpolarization component.
 8. The apparatus of claim 1, said first layerand said second layer of said meander line polarizer each comprising atleast one meander line constructive strip array positioned on a thindielectric at a 45 degree angle to a direction of said linearpolarization.
 9. The apparatus of claim 1, wherein an axial ratio ofsaid apparatus at a bandwidth greater than 500 MHz is 1 dB.
 10. Theapparatus of claim 1, wherein an axial ratio of said apparatus at abandwidth greater than 2 GHz is 2 dB.
 11. A flat plate antennaconfigured to perform dual circular polarization, comprising: anapparatus for performing dual circular polarization, including, a firstlinear polarization layer configured to perform a first sense of alinear polarization; a second linear polarization layer, positioned onsaid first linear polarization layer, configured to perform a secondsense of said linear polarization; a first meander line polarizer layerpositioned on said second linear polarization layer, and a secondmeander line polarizer layer positioned on said first meander linepolarizer layer, wherein said first meander line polarizer layer andsaid second meander line polarizer layer convert linear polarizationsignals output from said first linear polarization layer and said secondlinear polarization layer into circular polarization signals.
 12. Amethod of performing dual circular polarization, comprising the stepsof: (a) performing a first sense of linear polarization to generate afirst linearized output; (b) performing a second sense of linearpolarization to generate a second linearized output; and (c) receivingsaid first linearized output and said second linearized output in atwo-layer meander line polarizer to generate circular polarizationsignals.
 13. The method of claim 12, said (a) comprising: performingsaid first sense of said linear polarization in a first linearpolarization layer; and performing said second sense of said linearpolarization in a second linear polarization layer that is positioned onsaid first linear polarization layer.
 14. The method of claim 13,wherein at least one foam layer is positioned between each of said firstlinear polarization layer, said second linear polarization layer andsaid first layer and said second layer of said meander line polarizer.15. The method of claim 12, wherein a ground plane is positioned on asurface of said linear polarizer and opposite said meander linepolarizer.
 16. The method of claim 12, wherein said (a) comprisesgenerating a left hand circular polarization component, and said (b)comprises generating a right hand circular polarization component. 17.The method of claim 12, wherein said first layer and said second layerof said meander line polarizer each comprise at least one meander lineconstructive strip array positioned on a thin dielectric at a 45 degreeangle to a direction of said linear polarization.
 18. The method ofclaim 12, wherein an axial ratio of said apparatus at a bandwidthgreater than 500 MHz is 1 dB.
 19. The method of claim 12, wherein anaxial ratio of said apparatus at a bandwidth greater than 2 GHz is 2 dB.